Add test for System.arraycopy with different source/target indexes

tests/src/test/java/org/teavm/classlib/java/lang/SystemTest.java

@@ -15,6 +15,7 @@
  */
 package org.teavm.classlib.java.lang;
 
+import static org.junit.Assert.assertArrayEquals;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNull;
@@ -44,6 +45,28 @@ public class SystemTest {
         assertSame(a, dest[2]);
     }
 
+    @Test
+    public void copiesArrayPart() {
+        var a = new Object();
+        var b = new Object();
+        var src = new Object[] { a, b, a };
+        var dest = new Object[5];
+        System.arraycopy(src, 0, dest, 1, 3);
+        assertNull(dest[0]);
+        assertSame(a, dest[1]);
+        assertSame(b, dest[2]);
+        assertSame(a, dest[3]);
+        assertNull(dest[4]);
+
+        dest = new Object[5];
+        System.arraycopy(src, 1, dest, 0, 2);
+        assertSame(b, dest[0]);
+        assertSame(a, dest[1]);
+        assertNull(dest[2]);
+        assertNull(dest[3]);
+        assertNull(dest[4]);
+    }
+
     @Test
     public void copiesPrimitiveArray() {
         int[] src = { 23, 24, 25 };
@@ -54,6 +77,18 @@ public class SystemTest {
         assertEquals(25, dest[2]);
     }
 
+    @Test
+    public void copiesPrimitiveArrayPart() {
+        var src = new int[] { 23, 24, 25 };
+        var dest = new int[5];
+        System.arraycopy(src, 0, dest, 1, 3);
+        assertArrayEquals(new int[] { 0, 23, 24, 25, 0 }, dest);
+
+        dest = new int[5];
+        System.arraycopy(src, 1, dest, 0, 2);
+        assertArrayEquals(new int[] { 24, 25, 0, 0, 0 }, dest);
+    }
+
     @Test
     public void copiesToSubclassArray() {
         String[] src = { "foo", "bar", "baz" };